A cooler usually comprises a cooler block, which has a gas path through which the gas flow can flow and a coolant path through which a coolant can flow, the gas path and the coolant path being thermally coupled to each other in a media-separated manner.
Such coolers come into use in a varied manner in vehicles. A particular form of application is produced in the exhaust gas return, in which exhaust gas is fed from an exhaust gas system externally to a fresh air system, in order to mix the returned exhaust gas with the fresh air upstream of combustion chambers of an internal combustion engine. Such an exhaust gas return (EGR) has proved to be advantageous with regard to the fuel consumption and the pollutant emissions of the internal combustion engine. In turbocharged internal combustion engines, a differentiation is made between a high pressure exhaust gas return (HP EGR) and a low pressure exhaust gas return (LP EGR). A turbocharged internal combustion engine is equipped with an exhaust gas turbocharger, the turbine of which is arranged in the exhaust gas system and the compressor of which is arranged in the fresh air system. Here, the compressor and turbine divide the fresh air system and the exhaust gas system respectively into a high pressure region and a low pressure region. The low pressure region on the fresh air side extends upstream of the compressor. The high pressure region on the fresh air side extends downstream of the compressor. The low pressure region on the exhaust gas side extends downstream of the turbine. The high pressure region on the exhaust gas side extends upstream of the turbine. A high pressure exhaust gas return (HP EGR) therefore takes place upstream of the turbine and downstream of the compressor. In contrast thereto, a low pressure exhaust gas return (LP EGR) takes place downstream of the turbine and upstream of the compressor.
In the exhaust gas, water can be contained in the form of water vapour, which can arise through the combustion processes. Likewise, water can be contained in the form of water vapour in the fresh air drawn in from the environment. The returned exhaust gas is generally cooled by means of an exhaust gas return cooler, for example in order to increase the mass flow of the fresh air. Depending on the environmental conditions, the returned gas can cool here below the dew point of water, whereby a condensation can occur, so that therefore liquid water accumulates. Hereby, drops can form, which can damage components which follow downstream. Here, both mechanical and corrosive damage is possible. In particular, a compressor wheel, which rotates at a high rotation speed in the compressor, is exposed to an increased risk of damage through the collision with droplets. In addition, condensate can settle and, in unfavourable environmental conditions, can freeze. Here, also, in particular the compressor wheel is exposed to an increased risk.
The risk of a condensate formation is particularly critical in a low pressure exhaust gas return, because there the returned exhaust gas is regularly cooled to a lower temperature level than in a high pressure exhaust gas return.
Preferred forms of application of such coolers are therefore EGR coolers, which can be integrated into a low temperature cooling circuit (LT cooling circuit) for a particularly high cooling efficiency, i.e. into a liquid cooling circuit, preferably a conventional engine cooling circuit. Such LT EGR coolers can, in particular in utility vehicles, come into use in the HP region or in the LP region, so that the concern is then with LT HP EGR coolers or respectively LT LP EGR coolers.
Apart from the water vapour, the exhaust gas can additionally contain various combustion residues, which are present in particle form. In particular, the combustion residues can contain soot, mineral components, ceramic particles or silicates.
Coolers of the type named in the introduction can also be used in buildings, in particular for air-conditioning the room air. Further possibilities for use of such coolers are, for example, a battery cooling, e.g. in electric vehicles, or in connection with an air supply of fuel cells. In addition to liquids or respectively condensate, the respective gas flow can also contain solids, such as e.g. dust, silicates (e.g. sand) or organic substances.